It isn't necessarily a sign of rebellion against Iran's theocratic government, however. Musicians, including a woman violinist who performs underground, say they enjoy the freedom their off-the-record existence provides.

Many musicians fled in the 1980s after Iran's Islamic Revolution. Today, though government minders have allowed some pop concerts to go on, musicians say all the hassles and restrictions make playing underground easier.

"Are we underground because we want to oppose the system? No," musician Danial Izadi said. "We wanted to do what we loved to do."